Jet Lag East vs. West: Why East Is Worse
Last reviewed: July 2026
Most people recover faster after westward flights than after eastward flights — even though the time shift can be the same size. The reason lies in a quirk of your internal clock, and the right strategy depends exactly on which direction you're flying.
Your internal clock runs longer than 24 hours
The human day-night rhythm is naturally a bit longer than 24 hours. That's why it's easier for your body to stay awake longer and fall asleep later than to feel tired earlier. This is exactly what decides the direction.
Westward flight: delaying the clock
If you're flying west — say from Europe to the US — you need to stay awake longer. That fits your clock's natural tendency. Seek bright light in the late afternoon and evening and stay awake until local bedtime; this deliberately delays your rhythm.
Eastward flight: advancing the clock
Flying east — say from Europe to Asia — means you need to sleep and wake up earlier. This is the tougher direction. Get bright light in the morning, avoid it late at night, and ideally start going to bed earlier a few days before your flight.
FAQ
Is jet lag worse going east or west?
Generally east. Falling asleep earlier goes against your internal clock's natural tendency to stay awake longer — that's why adjusting after eastward flights usually takes longer.
Are there exceptions to the rule?
Yes. Pronounced night owls handle westward flights especially well, while extreme early risers sometimes find eastward flights less harsh. Your own chronotype shifts the rule a bit.
What about very large time jumps?
From about twelve hours onward, it's sometimes shorter to shift the clock in the opposite direction. The jet lag calculator automatically accounts for this and picks the faster direction.
The science behind it
Flyly's plan is based on the phase-response curve of circadian chronobiology — the same model used in sleep research and space medicine for shift work and time zone changes:
- Lockley & Czeisler — Circadian phase-response curve to light, Harvard Medical School
- NASA Ames Research Center — Circadian rhythm & alertness in aircrew
- Roenneberg et al. — Chronotype & social jetlag, University of Oxford
- Eastman & Burgess — How to travel the world without jet lag, Nature / Sleep Medicine Clinics
